Telephone system



May 27, 1930. J. l. BELLAMY TELEPHONE SYSTEM Original Filed Oct. 30, 1924 PNN Juhu 'Bellam Patented May 27, 1939 Unirse STATES PATENT OFFICE JOHN' I. LELLAMY, 0F BROOKFIELD, ILLINOIS, ASSIGNOR, BY MESNE ASSIGNMENTS, TO AUTOMATIC ELECTRIC INC., OF CHICAGO, ILLINOIS, A CORPORATION OF DELAWARE TELEPHONE SYSTEM Original application led October 30, 1924, Serial No. 746,730. Patent No. 1,712,643, dated May 14, 1929.

Divided and this application filed Aprii 24, 19225` The present invention relates to telephone systems in general, but is concerned more particularly with automatic telephone systems; and the broadgeneral object isthe production of a new and improved arrangement in an automatic telephone system em ploying rotary line switches and subscribers individual meters, whereby the rotary line switches are simpliiied and whereby the operation of the meters is made more positive.

This application is a division of my copending application filed October 30, 192.4, and allowed October 24, 1927, Serial No. 746,730, now Patent No. 1,712,643, May 14:, 1929.

An object of the invention is the produc tion of a rotary line switch of the nonhoming type having a line relay and a combined cut-oi` and switching relay, and having no interlocking` device such as is usually provided between the armatures of the two rellhe interlocking arrangement usually provided in rotary line switches of this type is for the purpose ofpreventing a complete operation of the combined switching and cutoif relay when a call is incoming to the line. It this is not done the switching relaypulls all the way up and extends the line through to whatever trunk the wipers happen to be standing on. In the improved line switch herein disclosed, however, this cannot happen because the wipers of the line switch are connected up only when both relays are operated.

Now, since the line relay must be operated for the wipers to be connected up, it is evident that the line relay must be maintained operated throughout a connection, from which it follows that if the standard bridge cutoff arrangement is to be used, the line relay must be locked up to the so called release-trunk conductor. Since this is done,

'A the line relay cannot extend ground over the release trunk conductor, as is done in standard practice to render busy a trunk line as soon as it is seized, because it it did so, the liney relay would be selilocling and would not release. Furthermore, the line relay is a Serial No. 272,381.

slow acting relay and it it were allowed to lock to the release trunk conductor without further provision it might not fall back responsive to the removal of ground potential at the end of a connection before the trunk line is again taken for use by another line switch, and be thereby locked in on a second connection. It is, therefore, an object of the invention to provide suitable circuit arrangements so that neither of the difficulties just outlined is encountered. This latter object is attained by providing a fourth wiper to gether with a cooperating multiple conductor, which is grounded as soon as a trunk line is seized, thereby making the trunk line busy immediately to other line switches and which is maintained grounded so as to prevent re-seizure of the trunk line until after the line relay has fallen back at the end of a connection.

In many installations it is considered good practice to provide a meter individual to each line at the exchange to record the total number of calls made over the associated line. This meter is operated ordinarily either by the so-called booster-battery method over the release trunk conductor of an established connection or over a separate conductor carried through a fourth wiper of the line switch. Now, if the metering is to be applied to a line switch such as outlined above, it will be necessary to provide a fifth wiper if the metering circuit is to be kept entirely separate from other circuits. This, however, while highly advantageous in case the only alternative is booster-battery metering over the release trunk conductor, is not at all necessary with the present arrangement for this reason: In the ordinary system, the release trunk conductor must be grounded and maintained grounded throughout the connection or else connected to a battery having a potential more positive than ground so as to insure that the trunk is maintained guarded at all times. lVith theV present arrangement, however, a seized trunk line is guarded through the fourth conductor thereof, which may be called a guarding conductor, so that the release trunk conductor becomes, for the most part, merely a holding conductor whose function is to hold up the line relay of the line switch. Under these circumstances, a resistance may be inserted into the release trunk conductor of the connection suihcient to limit the current How to a small value so that a meter connected in parallel with the line relay of the line switch will not operate until the resistance is short circuited by the usual polarized metercontrol relay, at which time a large increase in current is brought about so that the margin of operation is sufliciently great that no difficulty is experienced in maintaining the meter in adjustment.

It is a feature of the arrangement that the fourth conductor, which, as above outlined, is used for guarding purposes, does not need to be carried through to the first selector of the trunking system, but may be entirely local to the bank multiple of the rotary line switches. This means that a selector cannot be made busy to the rotary line switches at the selector itself over the guarding conductor. This, however, may be accomplished by grounding the release trunk conductor at the selector between the above-mentioned limiting resista-nce and the bank of the line switches and by means of the usual so-called test `iack.

Referring now to the accompanying drawing, it shows by means of the usual circuit diagrams a sullicient amount of equipment in a telephone system embodying the features of the invention to enable the invention to be understood.

The drawing shows the line switch LS in which the line at substation A terminates. This line switch is constructed in accordance with the features of the invention and it has access to the selector S, of which only the meter control relay 71, the jack J and the wipers are shown. The selector S has access to the connector C. which connector' in turn has access to lines, one of which is the line of substation B.

Mechanically, the line switch LS is of the well-known rotary type in which the wipers move in a forward direction only, are not restored to normal at the end of a connection, and are advanced upon the back stroke of the stepping magnet rather than upon the forward stroke.

In order to explain the operation of the apparatus shown. it will be assumed that the subscriber at substation A desires to converse with a subscriber at subst-ation B and that he removes his receiver and dials the number assigned to the line of substation B.

When the receiver is removed at substation A, a circuit is closed over line conductors 11 and 12 forline relay 16. Relay 16 operates and connects up the wipers 28-31 at armature springs 23, 24, 26, and 27, while at armature 25, it places a ground potential on the private normal conductor 13, thereby making the line of substation A busy to the connectors having access thereto, and closing a circuit through relay 15 and magnet 14 in series. The further operation depends upon whether the trunk line upon which the wipers of the line switch are standing is busy or idle. If this trunk line is busy, a ground potential is encountered by wiper 29 or by wiper 30, as vill be later explained, in which case relay 15 is short circuited and does not energize. Magnet 14 is operated, therefore, through its self-interrupting contacts to advance the wipers step by step in search of an idle trunk.

When an idle trunk is reached, for example, the trunk comprising conductors 36-38, no ground potential is encountered by either wiper 29 or wiper 30, with the result that relay 15, being no longer short-circuited, energizes in series with magnet 14. Magnet 14 does not operate at this time due to the relatively high resistance of relay 15. Upon operating, relay 15 at armature springs 18 and 22 disconnect conductors 11 and 12 from relay 16 and ground and extends them through wipers 28 and 31 by way of armature springs 23 and 27 of relay 16 to conductors 36 and 38 of the selector S, which conductors are normally connected within the selector to the usual line relay (not shown), similar to line relay 42 of the connector C. Relay 15 at armature 21 places ground on wiper 30 through arn'iature 26, thereby extending a ground potential to the multiple conductor 34, which is local to the bank multiple. This makes the trunk line busy immediately to the other line switches having access to it, because no line swit.h can seize this trunk line with a ground potential on the bank multiple conductor 34. At armature 20, relay 15 prepares a lockingl circuit for the slow-acting line relay 16 through armature spring 24, wiper 29, and release trunk conductor 37, while at armature 19 it places the marginally adjusted meter M in parallel with line relay 16.

When the line conductors of the line of substation A, are extended through as above mentioned to conductors 36 and leading to the switch S, the above mentioned line relay of the selector' S operates and closes a circuit for the associated release relay, also not shown, which release relay thereupon operates and places ground on release trunk conductor 37 in the usual manner, thereby establishing a holding circuit through resistance 84 and over conductor 37 for relay 16, which circuit includes wiper 29 and armature springs 24 and 20. Due to the relatively low potential impressed across its winding at this time, the marginally adusted meter M does not operate. This potential is low at this time owing to the inclusion of the resistance 84 in the release trunk conductor 37. It will be understood, of course, that this circuit is closed before the slow acting line relay 16 has had time to fall back,

and that, once operated, relay 16 will remain operated with only a very low potential imressed across its winding.

lVhen the release trunk conductor 37 is grounded at the selector S through the resis'tance Se, a circuit is closed from the release trunk conductor independent ot resistance 84 for the lower winding oi electro-polarized relay 71. Current is now l'lowing through both windings of this relay, the upper winding thereof being in parallel with resistance 83 through which the line relay of the selector S is energized. The electro-polarized relay is not operated at this time owing to the tact that the current flow in either winding is in a direction such as to odset the magnetic effect otl the current flow through the other winding.

In the case ot acall to the subscriber at substation B only three digits are required, the first to operate the selector S and the second and third to operate the connector C.

The selector S responds in the usual manner to the dialling ot the first digit and raises its wipers opposite the desired level of trunlr lines and seizes an idle trunk line, which trunk line will be assumed to be the one ei:- tending to the connector C. llhen this trunk line is seized, the usual switch-through operation takes place within the selector' S extending the line conductors as shown by the dotted connection to the wipers ot the selector, whereupon line relay 42 of thc connector C energizes over the calling line and through contacts of back bridge relay 41 and closes a circuit for release relay e3. Release relay 13 operates and places a ground potential on the associated release trunk conductor so as to hold up the established connection and at the same time prepares thc connector Yfor its operation.

VJhen the second and third digits are dialled, the wipers of the connector are positioned on the back contacts of the line ol substation B and ringing current is applied in the usual manner.

TWhen the receiver is removed at substation B, the usual ring-cubed relay (not shown) of the connector operates and switchesthe connection through asindicated by the dotted conductors associated with the wipers, whereupon back-bridge relay 41 opcrates, and reverses the current flo-w over the calling line. Electropolarized relay 71 now operates and short circuits resistance 84: at armature spring 85, and at armature spring 86 it short circuits resistance 83 and its own upper winding so as to afford a better talking circuit. The lower winding of relay 71 is sufficient to maintain the relay operated after the upper winding has been short circuited. As a result of the short circuiting of resistance 811, the current flow through line relay 16 and the marginal meter M is increased suiiciently to operate the meter M, which by means of the usual train of number wheels registers the call. The magnet of the meter M remains operated until the end of the connection. i

The two subscribers may now .converse with each other over the connection set up. llhen the conversation has terminated, they both replace their receivers. llVhen the receiver is replaced at substation B, backbridge relay l1 falls back and reverses the associated line-relay connect-ions to normal, but this is without particular eect at this time since the upper Winding ot the electro polarized relay 71 is short circuited at armature 86. It will be understood, of course, that in case armature 86 were omitted the upper winding would still be in circuit and that relay 71 would restore and remove the short circuit from around resistance 84. lith an ordinary adjustment, the meter M would remain operated, from which it follows that there would be no danger of several operations et the meter M in the latter case, even though the subscriber at substation B should replace and remove his receiver several times betere the release ot the con nection.

When the subscriber at substation A replaces his receiver, line relay 42 of the connector C falls back and permits the release of slow-acting release relay 13, whereupon the connector C is released and ground potential is removed from the associated release-trunk conductor. When thisoccurs the release of the selector S takes place in the usual manner and relay 71 alls back.

When the ground potential is removed from the release trunk conductor by relay 43 of the connector, the circuit of relay 16 ot the line switch LS is opened and the circuit of the meter M is opened. The meter M falls back right away, and slow acting relay 16 falls back a moment later. Relay 16 disconnects the wipers ot the line switch and opens the circuit of relay 15, whereupon relay 15 falls back. The trunk line extending to the selector S is maintained guarded by a ground potential applied through wiper 30 to conductor 34 until relay 16 has fallen back.

YWhen a call isreceivcd at substation A through the banks of a connector similar to the connector C, private normal conductor 13 is grounded by the seizing connector through the test wiper thereof, operating relay 15 to disconnect line conductors 11 and 12 from line relay 16 and ground. Since line relay 16 is not operated under these circumstances, the wipers 28-31 are not connected up, notwithstanding the complete operation of relay 1i',

lhat is claimed is:

1. 1n a rotary line switch having wipers which normally stand on the bank contacts, a line relay for initiating the hunting movement of said line switch, a combined switching and cut-olf relay for disconnecting the associated line from said line relay and for connecting it to the switch wipers when a call is made on the associated line, and for disconnecting the associated line from the line relay when a call is received on the associated line, a third wiper on said switch ior supplying current to hold up said line relay on an outgoing call to maintain the wipers connected up, a fourth test wiper for said switch, and circuit connections for supplying potential through the fourth test wiper to guard the selected set of back contacts.

2. In a trunk-hunting line switch, a line relay energized over the line to start thc hunting operation, a cut-off relay for disconnecting the line relay from the line when an idle trunk is found, means for maintaining the line relay energized over the selected idle trunk, and contacts on both the cut-off relay and the line relay for extending the line to the selected trunk,

3. In an automatic telephone system wherein each subscrihers line entering the exchange terminates in an individual rotary line switch, each line switch having a line relay energized over the calling line and a combined switching and cut-off relay energized under the control of the line relay, and contacts on both relays in series for connecting the calling line to the wipers of the switch.

4. In a telephone system wherein a rotary line switch having access to a plurality of trunk lines is provided with a line relay and a switching relay held operated by the line relay, a holding circuit for the line relay completed over a holding conductor of a seized trunk, a separate guard conductor multipled throughout the banks of a plurality of line switches, and means including a separate' wiper on each line switch for testing for idle condition on the guard conductor and for placing a busy potential on the guard conductor of any seized trunk line.

5. In a telephone system wherein a rotary line switch having access to a plurality of trunk lines is provided with a line relay-and a switching relay held operated by the line relay, a holding circuit for the line relay completed over a holding conductor of a seized trunk, a separate guard conductor niultipled throughout the banks of a plurality of line switches, means including a separate wiper on each line switch for testing for idle condition on the guard conductor and for placing a husy potential on the guard conductor of any seized trunk line, a registering device connected in circuit with the line relay of an operated line switch, a resistance in series with the holding conductor, and means for short cireuiting said resistance upon the response of a called subscriber for operating said register to record the completed connection.

6. In combination,a hunting switch having two test wipers and two sets of bank contacts over which said wipers are arranged to travel, respectively, while the switch is hunting, means including said two test wipers and ctl'ective during the limiting operation of the switch for making a simultaneous test of both contacts of a pair encountered by the two test wipers, and means responsive to the non-engaged condition found on a pair of contacts for stopping the hunting movement of the switch and for marking only one contact engaged.

7. In combination, a limiting switch having two test wipers and two sets of bank contacts over which said wipers are arranged to travel, respectively, while the switch is hunting, means including said two test wipers and eti'ective during the hunting operation of the switch for making a simultaneous test of both contacts of a pair encountered by tlie two test wipers, means responsive to the non-engaged condition found on a pair of contacts for stopping the hunting movement of the switch and for marking only one terminal engaged, and means external to said switch for marking the other terminal engaged at will.

8. In a telephone system wherein a hunting switch has access to a plurality ot trunk lines through its movable wipers and stationary bank contacts, a registering device arranged to be operated through a register wiper and cooperating bank contact and corresponding operating conductor of a seized trunk line, said switch having also a test wiper arranged to test trunk lines over their test conductors during the hunting movement of the switch, and circuit arrangements in said switch for also testing thc trunk lines over the said operating conductors.

9. In a telephone system wherein a trunk hunting switch has access to a plurality of trunk lines through its movable wipers and stationary bank contacts, registering device arranged to be operated through a register wiper and cooperating bank contact and corresponding conductor of the seized trunk line, said switch having also a test wiper arranged to test trunk lines over their test conductors during the hunting movement of the switch, circuit arrangements in said switch for also testing the trunk line over the said operating conductors, and means associated with said trunk lines for applying a guarding potential to any of said operating conductors at will.

In witness whereof, I hereunto subscribe my name this 23rd day of April, A. D. 1928.

JOHN I. BELLAMY. 

